In accordance with the trend of thin monitor and TV, the demand for high voltage IC of plasma/LCD panel is increasing rapidly. In order to maintain the quality and yield of the high voltage IC, testing the high voltage IC after mass production is necessary. However, the high voltage IC has outputs up to 80V˜100V and even higher, but a conventional low voltage logic tester is equipped with a power supply below 40V, and provides an output comparator level lower than 12V. If a special designed high voltage logic tester is employed to test the high voltage IC, it is apparent that the testing cost will increase dramatically.